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Electronic Properties of Oxide and Semiconductor Heterostructures
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| 자료유형 | 학위논문 |
|---|---|
| 서명/저자사항 | Electronic Properties of Oxide and Semiconductor Heterostructures. |
| 개인저자 | Sammon, Michael Joseph. |
| 단체저자명 | University of Minnesota. Physics. |
| 발행사항 | [S.l.]: University of Minnesota., 2019. |
| 발행사항 | Ann Arbor: ProQuest Dissertations & Theses, 2019. |
| 형태사항 | 143 p. |
| 기본자료 저록 | Dissertations Abstracts International 81-05B. Dissertation Abstract International |
| ISBN | 9781687985651 |
| 학위논문주기 | Thesis (Ph.D.)--University of Minnesota, 2019. |
| 일반주기 |
Source: Dissertations Abstracts International, Volume: 81-05, Section: B.
Advisor: Shklovskii, Boris. |
| 이용제한사항 | This item must not be sold to any third party vendors. |
| 요약 | The modern world's dependency on electronics provides a constant need to discover new materials and devices. A promising technique to fabricate a new device is to create a heterostructure |
| 요약 | {12/7}$. We show that such a long tail of $n(x)$ causes the magnetization and the specific heat of the accumulation layer to diverge at large $x$. We explore the truncation of the tail by the finite sample width $W$, the transition from the nonlinear to linear dielectric response with dielectric constant $\\kappa$, and the use of a back gate with a negative voltage $-\\abs{V}$. We find that as a result both the magnetization and specific heat are anomalously large and obey nontrivial power law dependences on $W$, $\\kappa$, or $\\abs{V}$. In the linear dielectric regime under a strong magnetic field, the large dielectric constant of STO makes it easy to reach a quasi-one-dimensional state known as the extreme quantum limit (EQL) in which all electrons occupy the lowest Landau level. We present a theory of the EQL phase in STO accumulation layers.We find a phase diagram of the electron gas in the plane of the magnetic field strength and the electron surface concentration for different orientations of the magnetic field. In addition to the quasi-classical metallic phase (M), there is a metallic EQL phase, as well as an insulating Wigner crystal state (WC). Remarkably, the insulating Wigner crystal phase depends on the orientation of the magnetic field. We show that these effects can be measured through quantum capacitance measurements of the STO accumulation layer. The third material we study is semiconducting quantum wires. Though it is not a heterostructure, it supports a low dimensional electron gas which is often tuned with an external gate, making it similar to many of the devices we have studied. We have theoretically investigated the influence of interface roughness scattering on the low temperature mobility of electrons in quantum wires when electrons fill one or many subbands. We find the Drude conductance of the wire as a function of the linear concentration $\\eta$ has a sharp peak. The height of this peak grows as a large power of the wire radius $R$, so that at large $R$ the conductance $G_{max}$ exceeds $e. |
| 요약 | 2/h$ and a window of concentrations with delocalized states (which we call the metallic window) opens around the peak. Thus, we predict an insulator-metal-insulator transition with increasing concentration for large enough $R$. Furthermore, we show that the metallic domain can be sub-divided into three smaller domains: 1) single-subband ballistic conductor, 2) many-subband ballistic conductor 3) diffusive metal, and use our results to estimate the conductance in these domains. Finally we estimate the critical value of $R_c(\\mathcal{L})$ at which the metallic window opens for a given length $\\mathcal{L}$.We conclude the thesis with a discussion of a newer class of materials known as transition metal dichalcogenides (TMDs).We study a capacitor made of three monolayers TMD separated by hexagonal boron nitride (hBN). We assume that the structure is symmetric with respect to the central layer plane. The symmetry includes the contacts: if the central layer is contacted by the negative electrode, both external layers are contacted by the positive one. As a result a strong enough voltage $V$ induces electron-hole dipoles (indirect excitons) pointing towards one of the external layers. Antiparallel dipoles attract each other at large distances. Thus, the dipoles alternate in the central plane forming a 2D antiferroelectric with negative binding energy per dipole. The charging of a three-layer device is a first order transition, and we show that if $V_1$ is the critical voltage required to create a single electron-hole pair and charge this capacitor by $e$, the macroscopic charge $Q_c = eSn_c$ ($S$ is the device area) enters the three-layer capacitor at a smaller critical voltage $V_{c} < V_{1}$. In other words, the differential capacitance $C(V)$ is infinite at $V = V_{c}$. We also show that in a contact-less three-layer device, where the chemically different central layer has lower conduction and valence bands, optical excitation creates indirect excitons which attract each other, and therefore form antiferroelectric exciton droplets. Thus, the indirect exciton luminescence is red shifted compared to a two-layer device. |
| 일반주제명 | Condensed matter physics. |
| 언어 | 영어 |
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: 이 자료의 원문은 한국교육학술정보원에서 제공합니다. |
